Secure Multi-Antenna Cognitive Wiretap Networks

Abstract

In this paper, we investigate the secrecy performance of a multiantenna cognitive wiretap network, where the secondary transmitter (Alice) communicates with the secondary receiver (Bob) in the presence of an eavesdropper (Eve). Specifically, we consider both half-duplex (HD) and full-duplex (FD) operations. For the HD, maximal-ratio combining (MRC) is adopted at Bob, while for the FD, we propose two jamming schemes to deteriorate the quality of the eavesdropper's channel, i.e., selection combining/selection jammer (SC/SJ) and SC/zero forcing beamforming (SC/ZFB). Assuming Rayleigh fading, exact closed-form expressions for the secrecy outage probability of the cognitive wiretap network are derived. In addition, we also provide simple asymptotic approximations for the secrecy outage probability under two distinct scenarios, depending on the quality of the main and wiretap channels. From the analytical results and numerical simulations, it is concluded that all the proposed schemes outperform the SC scheme; all the proposed schemes achieve full diversity when the main channel is much better than the eavesdropper's channel; MRC outperforms SC/SJ and SC/ZBF in the low interference threshold regime, while the opposite holds in the high interference one; and SC/ZFB always achieves better performance than SC/SJ, albeit with higher complexity.